The Planets

This is an introduction to the Solar System, its formation, and composition,
with special emphasis on the "terrestrial" or "inner" planets. I take a kind of
historical approach, noting the patterns and regularities
observed, for example, by Tycho Brahe, described by Johannes Kepler, and
explained by Sir Isaac Newton. Laplace and even the philosopher Immanuel Kant
figure into shaping our modern-day notions of the origin and composition of the
solar system.

"Early attempts to explain the origin of this system include the nebular
hypothesis of the German philosopher Immanuel Kant and the French astronomer and
mathematician Pierre Simon de Laplace, according to which a cloud of gas broke
into rings that condensed to form planets." - Encarta,
http://encarta.msn.com/encyclopedia_761557663/Solar_System.html

Taking the point of view of a first-time visitor, one of the first things you
would notice about the Solar System is that the spacing
between the planets' orbits consistently increases as you move away from the Sun
(with one exception). Furthermore, it's not a linear
increase, so we need essentially two figures, at different scales, to
represent the solar system (pictures courtesy of "The Nine Planets"):

Inner:

Outer:

Titius-Bode's law: Distance, r, of the nth planet from the Sun (in A.U.s) is
given by:

rn = 0.4 + 0.3 x 2n

Planet

n

rn

Actual

Mercury

-infinity, -1

0.4, 0.55

0.39

Venus

0

0.7

0.72

Earth

1

1.0

1.0

Mars

2

1.6

1.52

Asteroids

3

2.8

-

Jupiter

4

5.2

5.2

Saturn

5

10.0

9.6

Uranus

6

19.6

19.2

Neptune

7

38.8

30.1

Pluto

8

77.2

39.4

The Titius-Bode law was used to help discover Ceres, a 1000 km asteroid,
in 1802, and Uranus in 1781.

Check satellites of Saturn and Jupiter

Law has never been given a scientific foundation, and may be "chance,"
combined with the fact that the outer planets are larger (more on why later),
and hence "take up more room."

May have hindered models of Solar System formation as an arbitrary
constraint (Brahic, Formation of Planetary Systems)

Angular Momentum

Moment of inertia for planet spinning on its own axis, given above. For
body orbiting primary, consider body a point mass, so I = mr2

Albedo is the
fraction of light that is reflected by a body or surface.
It is commonly used in astronomy to describe the reflective properties of
planets, satellites, and asteroids.

Albedo is usually differentiated into two general types:
normal albedo and bond albedo.
Normal albedo, also called
normal reflectance, is a measure of a surface's relative brightness when
illuminated and observed vertically. The normal albedo of
snow, for example, is nearly 1.0, whereas that of
charcoal is about 0.04. Investigators frequently rely on observations of
normal albedo to determine the surface compositions of satellites and asteroids.
The albedo, diameter, and distance of such objects together determine their
brightness. If the asteroids Ceres and Vesta, for
example, could be observed at the same distance, Vesta
would be the brighter of the two by roughly 10 percent. Though
Vesta's diameter measures less than half that of Ceres,
Vesta appears brighter because its albedo is about 0.35, whereas that of Ceres
is only 0.09.

Bond albedo, defined as the
fraction of the total incident solar radiation reflected
by a planet back to space, is a measure of the
planet's energy balance. (It is so named for the American astronomer
George P. Bond, who in 1861
published a comparison of the brightness of the Sun, the Moon, and Jupiter.) The
value of bond albedo is dependent on the spectrum of the
incident radiation because such albedo is defined over the entire range
of wavelengths. Earth-orbiting satellites have been used to measure the
Earth's bond albedo. The most recent values
obtained are approximately 0.33. The
Moon, which has a very tenuous atmosphere and no
clouds, has an albedo of 0.12. By contrast, that of
Venus, which is covered by dense clouds, is
0.76.[http://zebu.uoregon.edu/~js/glossary/albedo.html]